151 Towards Better Tsunami Mitigation

8/10/2019 151 Towards Better Tsunami Mitigation

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TOWARDS BETTER MITIGATION OF TSUNAMI

DISASTER IN INDONESIA

Dinar C. ISTIYANTO1, Shigenobu TANAKA2, Toshio OKAZUMI3, SYAMSIDIK4

1Specialist Researcher, International Centre for Water Hazard and Risk Management,

Public Works Research Institute, Tsukuba, Japan, [email protected]

Deputy Director, International Centre for Water Hazard and Risk Management,

Public Works Research Institute, Tsukuba, Japan, [email protected]

3 Chief Researcher, International Centre for Water Hazard and Risk Management,Public Works Research Institute, Tsukuba, Japan, [email protected]

4Researcher, Tsunami and Disaster Mitigation Research Center,

Syiah Kuala University, Banda Aceh, Indonesia, [email protected]

ABSTRACT: This paper describes the tsunami disaster mitigation development in

Indonesia, especially related to its basic framework, its implementation and response totsunami disaster happened after 2004. The potential of tsunami intensity as hazard

identifier is also discussed. Lesson learnt from the two recent tsunami events, i.e.

Southern-West Java tsunami 2006 and Mentawai tsunami 2010 will be used to discussabout the significant role of land use management as well as education, training and drill

in the reduction of fatalities during tsunami disaster.

Key Words: Indonesia, tsunami disaster mitigation, emergency communication and

transportation, tsunami danger and precursor knowledge, maintenance of

tsunami early warning system, preparedness

INTRODUCTION

Historical data on tsunami disaster indicate that Indonesia is the most tsunami vulnerable country

in the world. In total, 110 fatal tsunamis occurred in Indonesia during 1600-2011, which causedcasualties and have killed about 244,000 people in total. This total human toll is unfortunately so far

the highest in the world, which indicates the high level of vulnerability of Indonesia against tsunami.Consequently, serious effort towards effective tsunami disaster mitigation in Indonesia is urgent.

Figure 1 shows the big-six countries or region with the highest total human casualties due to tsunamidisasters within the years of 1600-2011 (ITDB, 2006; Watanabe, 1985; NAO, 2004).

The huge disasters by the 2004 Indian Ocean Tsunami (IOT) that threaten countries surrounding

Indian Ocean stimulated the world cooperation in the development of Indian Ocean Tsunami EarlyWarning System (IOTEWS). At the same time countries around Indian Ocean, including Indonesia,

have been impelled to develop or enhance their disaster management system.

The fundamental revolution on disaster management paradigm in Indonesia was officially startedafter the enactment of Disaster Management Law in 2007. This law clearly mentions that disaster

Proceedings of the International Symposium on Engineering Lessons Learned from

the 2011 Great East Japan Earthquake, March 1-4, 2012, Tokyo, Japan

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management includes all three phases of disaster, i.e. before disaster (preparedness),

immediate-response actions during and after disaster (emergency), and after disaster (recovery and

reconstruction).In the Indonesian Disaster Management Law 2007, disaster mitigation is classified to be the

measure before disaster and includes the activities of (a) land use management, (b) developmentplanning, infrastructure development, building code, and (c) education, training and drill.

Implementation of these activities required knowledge of risk including risk mapping. To provide

accurate information about the risk, understanding about hazard characteristics is the primerequirement.

In the simplest approach, the tsunami hazard maps were drawn based on the historical data oftsunami wave height available for each area, which is finally classified into high medium low

tsunami hazard area. However, such a hazard map may not fully provide the necessary information

because the actual disaster is not merely dependent on wave height but are also affected by localtopography, demography, landuse, etc. Disaster mitigation planning needs more specific information to

enable detail action. In this concern, this paper is trying to provide hazard identification by using

tsunami intensity, based on which disaster mitigation activities can be determined easier.Lesson learnt from the two recent tsunami events, i.e. Southern-West Java tsunami 2006 and

Mentawai tsunami 2010 will be used to discuss about the significant role of land use management as

well as education, training and drill in the reduction of fatalities during tsunami disaster.

POTENTIAL OF TSUNAMI HAZARD IN INDONESIA

Hamzah et.al (2000) divided Indonesia into 6 zones (see Fig.2) by considering the composition of its

tectonic plate-convergence, the depth of seismicity variation, and the characteristics of tsunami

generation. It is described that in Zone-A most of tsunamis were generated by earthquakes as results ofthe activities of two tectonic elements; (i) subduction of Indian Ocean Plate beneath the Eurasian Plateand (ii) the great Sumatera fault located in Sumatera from its southernmost part near the Sunda Strait

to its northernmost part near the Andaman Island. Two tsunamis were generated by volcanic eruption

of Krakatau in 1883 and 1928.In Zone-B, tsunamis were generated by two types of earthquake, i.e. subduction of Indian Ocean

Plate beneath the Eurasian Plate and back-arc- thrusting lies east-west in the north of the

Bali-Lombok-Sumbawa Islands. One volcanic tsunami was caused by the eruption of Tambora in1915.

In Zone-C, all tsunamis were caused by tectonic earthquake due subduction of the Australian Plate

beneath the southeastern part of the Eurasian Plate except two by volcanic eruption of Rokatenda in1927 and 1928 and one tsunami by landslide at Lomblen.

Fig.1 The big-six countries or region with the highest total human casualties due to tsunami

disasters within the years of 1600-2011 (ITDB, 2006; Watanabe, 1985; NAO, 2004).

1600-2011

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In Zone-D all tsunamis were generated by earthquakes in the back-arc opening zone in theMakassar Strait, in which earthquakes usually have normal fault mechanism.

In Zone-E, within all tsunamis, four tsunamis were generated by volcanic eruptions, i.e. Awu in

1856 and 1892, Ruang in 1889, and Gamalama in 1871. The remaining tsunamis were generated byearthquakes in the Molucca Sea collision zone.

In Zone-F, tsunamis were generated by shallow earthquakes associated with the activity of

Caroline subduction zone.Based on the tsunami data provided by International Tsunami Data Base (WinITDB) developed by

Gusiakov et.al (2006), Hamzah et.al (2000), Widjo et.al (2006) and Hidayat et.al (2007) a decadaltsunami events statistic in Indonesia was drawn. In Fig.3, these data are shown as bar graphs

corresponding to each zone (A, B, C, D, E, and F) marked in Fig.2.

Fig.2 Seismotectonics zonation of Indonesia Region, which is divided into six

zones (Zone-A, B, C, D, E, and F). Yellow lines denote the boundariesof each zone. (Source: Hamzah et al., 2000)

0 5 1 0

1601 1610

1611 1620

1621 1630

1631 16401641 1650

1651 1660

1661 1670

1671 16801681 1690

1691 1700

1701 1710

1711 1720

1721 17301731 1740

1741 1750

1751 1760

1761 17701771 1780

1781 1790

1791 1800

1801 18101811 1820

1821 1830

1831 18401841 18501851 1860

1861 1870

1871 1880

1881 18901891 1900

1901 1910

1911 1920

1921 19301931 1940

1941 1950

1951 1960

1961 19701971 1980

1981 1990

1991 2000

2001 2010

0 5 10 0 5 10 0 5 10 0 5 10 0 5 1 0

Fig.3 Decadal tsunami event statistics in Indonesia based on ITDB data (Gusiakov et.al. 2006) plus

the latest data. Red-stars mean tsunami with I > 2.5 or those caused si nificant fatalities,whereas green-stars indicate tsunami with I < 2.5 but caused considerable fatalities in the area.

B CD

FE

Indo-Australian Plate

Philippine Sea

Plate

Eurasian Plate

aroline

late

ustralia

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In Zone-A, very few records are available on tsunami wave height or fatalities except after the2004. However, it could be noticed that the recurrence of tsunami with intensity of 2.5 or higher is

learned to be happened about every 100 to 150 years. The following events were reported to cause

high Tsunami Intensity (I) or cause big fatalities (F) or damage, i.e. in 1797 (I=3), 1833 (I=2.5), 1861(I=3, F=725), and 2004 (I=4, F=165,000).

In Zone-B, the recurrence of tsunami with intensity of 2.5 or higher is about every 30 to 50 years.

The following events are considered to have significant level of hazard or disaster, i.e. 1818 (I=3.5,F=400), 1851 (Hmax=14.5), 1883 (Hmax=36, I=4.5, F=36,417), 1917 (F=15,000), 1977 (I=3.5,

F=189), 1994 (I=2.5, F=250), and 2006 (I=2, F=390).Zona-C is the most active tsunami zone with the long record since 1629. It is seen that tsunamis

with intensity of 2.5 or higher have happened about every 50 to 80 years. They were including the

events of 1629 (I=3), 1674 (I=4, F=2,970), 1763 (I=2.5), 1852 (I=2.5), 1899 (I=3), 1928 (I=3), 1979(I=3, F=539), and 1992 (I=2.7, F=2,200).

Zone-D is the most less tsunami hazard area in Indonesia. Only five tsunami events were reported

since 1917 and the tsunami intensities I are less than 1.5. However, fatalities of 13 people werereported in the event of 1967.

In Zone-E, the recurrence of tsunami with intensity of 2.5 or higher is about every 40 to 50 years.

Although the fatalities were not as huge as those in Zone-A, B, or C, there were four records oftsunami events with tsunami intensity equal or greater than I=2.5, i.e. 1889 (I=2.5), 1927 (I=3, F=50),

1968 (I=3, F=392). In addition, in 1856, smaller tsunami with I=2 caused fatalities of F=100.

Zone-F booked more tsunami event comparing to Zone-D but the recorded maximum tsunamiintensity are only between 1.5 and 2. The most fatal tsunami disasters in this area happened in 1864

(I=1.5, F=250) and 1996 (I=1.8, F=108).

Tsunami Intensity Variation in Indonesia

From the same source of data (Gusiakov, 2006), correlation of tsunami intensity with its incidentnumber for each area was drawn as in Fig.4. The tsunami intensity scale is of Soloviev-Imamura

(1972). It is shown that, except Zone-D and F, most of Indonesian region experienced tsunami hazards

with high intensities of greater than I=4. In Zone-D and F the maximum tsunami intensity is only I=2.It can also be seen that in all area, the most frequent events are those with tsunami intensity between

I=1 and 1.5.

A rough approximation of the exceedence probability graphics of tsunami intensity were generated

from the available data. Since the data in Zone-A, B and E show a similar tendency, the data of thesezones are combined to get the graphic for the related zones and is provided in Fig.5(left). The similar

Fig.4 Correlation of tsunami intensity with its incident number for each area.

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graphic for the combined Zone-C and F is shown separately in Fig.5(right). No graphic is provided forZone-D as the data for this zone is too few. From Fig.5 we learned that the median tsunami intensity inall zones are about I=1.5.

Based on the above discussion, tsunami intensity I=1.5 (Soloviev-Imamura scale) shall be set-up as athreshold for minimum design criteria of any mitigation measure in all area of Indonesia, whereas the

maximum design criteria is adjusted to the relevant area.

Typical Exposure and Vulnerability against Tsunami Disaster in Indonesia

The exposure of coastal area against tsunami shall be assessed by considering the distance of vitalassets (residential area, factory, city infrastructures, etc.) to coastline, the altitude of the area above

mean sea level, and availability of protective measure (Post, 2007). Whereas, population density,

building structures, and building density have been considered as several important factors related to

vulnerability.Most of coastal cities or village in Indonesia traditionally lay very close to coastline without any

protective structure against high wave. Many of them are also located along the river bank from the

river mouth into inland direction. At several parts of coastal areas, seawall or revetment had been

constructed but for the purpose of coastal erosion countermeasure only.Further, referring to the description by McGranahan et al. (2006), 20% of Indonesian populations

(about 40 millions) are living along coastal areas that fall under the criterion of Low Elevation Coastal

Zone (LECZ). McGranahan et al. define the LECZ as contiguous land area up to 100 kilometers fromthe coast that is ten meters or below in elevation. This situation increases the exposure grade of

Indonesian coastal areas against tsunami hazard.

Referring to Tsunami Hazard Map of Indonesia (Paris, 2007), the following areas are classifiedinto very high and high tsunami hazard area: western-coast of Sumatera, from Banda Aceh to

Lampung; west and southern coast of West-Java; southern-east coast of East-Java; northern coast ofBali, north-eastern coast of Flores and islands north to Timor Island; northern coast of Papua Island;western coast of Central Sulawesi; and coastal areas surrounding Halmahera Sea, Sulawesi Strait, and

Seram Sea.

Figure-8(a) and -8(b) respectively show the Googles bird view of Padang City and Bengkulu City,the two most populated coastal cities along western-coast of Sumatera Island. These figures show high

level exposure of those two cities against tsunami disaster by fact that these cities are linked to the sea

without any protection at all. Refer to the map of population density within the LECZ provided byCIESIN (2007), Padang as well as Bengkulu cities are occupied by 500 to 1,000 residents within a

kilometer square of its LECZ. According to Borerros worst scenario simulation (2006), the futuregiant tsunami will inundate about 8 km coastline of Padang City up to 1.5 km inland, whereas about

11 km of Bengkulu Citys coastline will be inundated between 400m to 1.5 km inland.

Fig.5 Graphics of probability of exceedence of tsunami intensity for: (left) zones of A+B+E; and(right) zones of C+F

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TSUNAMI EVENTS IN INDONESIA AND IMMEDIATE E VACUATION RESPONSE

Systematic investigations on tsunami disasters in Indonesia were started just after the Flores Tsunami

in 1992. This is the first devastating tsunami in the modern age of Indonesia with fatalities toll of

about 2,200. Twenty-five tsunami events were reported happened in Indonesia since then, however,not all events caused casualties or fatalities, and some others were not recorded in detail. Table 2

shows tsunami events in Indonesia since the Flores Tsunami in 1992.

Table 2. Tsunami events in Indonesia 1992-2011

Year Month Date Time Lat Long Ms I Hmax D Fatal WS Zone

1992 12 12 13:29 -8.48 121.9 7.5 2.7 26.18 L 2200 TIB C

1994 1 21 11:24 1.01 127.73 7.3 1.5 2 L N/A F1994 2 15 17:07 -4.97 104.3 7 TIB

1994 6 2 01:17 -10.48 112.83 7.2 2.5 13.9 L 250 TIB B

1994 10 8 06:44 -1.26 127.98 6.8 1.5 3 M 1 TIB F

1995 2 13 15:42 -1.32 127.44 6.8 0 TIB

1995 5 14 11:33 -8.38 125.13 6.9 1.5 4 M 11 TIB C

1996 1 1 16:05 0.73 119.93 7.7 1.8 3.43 M 24 TIB E

1996 2 17 14:59 -0.89 136.95 8.1 1.8 7.68 M 108 RTW F

1998 11 29 14:10 -2.07 124.89 7.6 1.5 2.7 N 0 RTW E

2000 5 4 12:21 -1.11 123.57 7.5 1 5 S 0 TIB E

2000 6 4 16:28 -4.72 102.09 8 N 0 TIB

2000 6 18 14:44 13.8 97.45 7.8 N 0 NOW

2002 9 13 22:28 13.04 93.07 6.7 0 N 0 TIB2002 10 10 19:50 -1.76 134.3 7.7 1 3 N 0 TIB F

2004 11 11 21:26 -8.17 124.91 7.5 1 2 N 0 C

2004 12 26 7:58 3.32 95.85 9 4 15 L 165,000 NOW A

2005 3 28 23:09 2.06 97.01 8.7 1.5 4 L TIB A

2005 4 10 11:14 -1.71 99.78 6.5 -2.5 0.4 N 0 A

2005 7 24 15:59 7.9 92.1 7.2 TIB

2006 3 14 15:57 -3.6 127.21 6.6 2 5 L 3 TIB C

2006 7 17 15:19 -9.33 107.27 7.7 2 2 390 LTW B

2007 9 12 13:10 -4.52 101.37 3 3.9 S 0 LTW A

2009 1 3 19:43 -0.408 132.89 7.7 0

2010 10 25 14:42 -3.484 100.114 7.7 3.3 9 L 530 PTW A

a

b

Fig.8 Googles bird view of (a) Padang City and (b) Bengkulu City, the two most populated coastalcities along western-coast of Sumatera Island.

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In Table 2, Ms is surface magnitude of the earthquake, I is tsunami intensity scale of

Soloviev-Imamura, Hmaxis themaximumobserved run-up value,D is damage classification ingeneral, Fatalis number of killed people, WSmeans whether a warning message was released or not.In the WS column, NOW - no warning was issued, PTW - Tsunami Warning issued by Pacific

Tsunami Warning Center, RTW - Regional Tsunami Warning issued by PTWC for areas having noTWS, LTW - Local Tsunami Warning issued by regional or national TWC, TIB Tsunami

Information or Attention Bulletin issued by any agency, N/A - status unknown).

Among those events, 15 events (shaded line in Table 1) were selected and used to draw diagram asshown in Figure-6. It shows number of killed people, tsunami intensity, effective local warning status,

status of immediate evacuation action, initial tsunami arrival time and its lead time after earthquake in

each tsunami events.

Killed people means number of people directly killled by the disaster. Effective warning means

whether a local warning disseminated and reach to the residents effectively just before the disasters. If

local warning was disseminated, then it is given the value of 1, whereas value of zero is given in caseof no local warning at all. Meanwhile, immediate evacuation means whether the residents evacuated

immediately after sensed the earthquake shaking. Value of zero means no evacuation, value of 0.5means very few people were evacuated, and value of 1 is given to the events where many peopleimmediately evacuated just after the earthquake or local warning.

Based on Figure-6, it is learnt that since 1992 only one local warning was effectively worked

before tsunami disaster events (i.e. Bengkulu Tsunami, 2007).Figure 6 also shows that immediate evacuations by most of the residents were conducting only in

four events (with or without local warning, i.e. 1998, 2005, 2006, 2007), very few evacuation were in

three events (without local warning, i.e. 1996, 2004, 2010) and the remaining events performed noimmediate evacuation responses. This distribution is summarized in Figure-7.

It can also be seen in Fig.6 that immediate evacuation related to few or no fatalities due to tsunami.On the opposite, several to huge number of fatalities were recorded related to no or very few

immediate evacuations. Although many other factors, such as coastal morphology, tsunami intensity,

Fig.6 Number of killed people, tsunami intensity, effective local warning status, status of immediateevacuation, initial tsunami arrival time and its lead time after ea thquake in 14 tsunami event in

Indonesia within 1992-2011.

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distance of residential area from the coastline, availability of coastal protection, etc. also have theirroles however, these facts have given indication on the significance of immediate evacuation in

reducing the fatalities due to tsunami disaster.

At the top part of Fig.6, the dark circles sign for tsunami event between 21:00 to 07:00, emptycircles sign for tsunami event between 07:00 to 18:00, and half-dark circles sign for the event between

18:00 to 21:00. The cases of Taliabu (1998) and Nias (2005) shows that people did immediateevacuation even if the hazard is generated in the midnight. It seems that their correct understanding on

the danger of tsunami and high awareness have led them to perform effective response.

SOUTH-WEST JAVA TSUNAMI 2006, EFFECTIVE WARNING AND AWARENESS

A tsunami disaster was generated along the west and central southern coast of Java Island on 17 July

2006 due to a tsunami earthquake (Mw = 7.7) that occured offshore near the trench of the Sunda

subduction zone south of Java at about 3:19 p.m. local time. The local felt reports indicated only weak

shaking in Java. There was no ground motion damage from the earthquake, but there was extensivedamage and loss of life from the tsunami (Mori et al., 2007). Figure 9 shows the map of the earthquake

epicenter location (USGS, 2006).

Despite having had learnt the great lesson from the IOT 2004, this disaster, however, still recorded

464 human tolls. The less awareness as well as less understanding of local community on the various

types of tsunami precursor has caused this unexpected number of human toll.There was no effective local tsunami warning system in place, whereas the national warning

dissemination system had not ready yet. This caused the warning messages did not reach the target

residents. This claim was supported by a questionaire based survey result reported by Muhari et al.(2007), which concluded that more than 70% of the residents in four locations among the five

Fig.9 Map of the earthquake epicenter location

Legend:the most affectedcoatal

ine (Widjo et al.,2006)

BALI

Jakarta

JAVA

EQ Epicenter

(USGS, 2006)

INDIAN

OCEAN

Christmas Is. 100 km

effective warning

1 (7 %)

no effective warning14 (93 %)

no immediateevacuation

8 (53 %)

many immediate

evacuation4 (27 %)

few immediateevacuation

3 (20 %)

Fig.7 Distribution graphs of number of tsunami disaster events with or without local effectivewarning (left) and number of tsunami events with or without immediate evacuation response

(right). Case of Indonesia (selected) 1992-2011.

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surveyed locations heard no evacuation warning related to this tsunami.Such a situation can beunderstood by refering to Table 2, which shows part of the warning time-line of South-West Java

Tsunami of 2006 compiled by IOC-ITIC (2006). It is known from this record that initial detection of

potential tsunami and warning initiatives were well performed by the Indonesian national authority.However, a failure to contact local government official by telephone due to unavailability of

communication contact points at the respected coastal area is considered to have fluffed the effective

early warning (see line no.6 in Table 1). This has taught the importance of ensuring warningdissemination link until the end node of disaster target. Regular updating of contact point data is

comparably important measure to facilitate smooth warning dissemination.Furthermore, the residents knowledge on various types of earthquake characteristics and their

possibility in generating tsunamis, such as this tsunami earthquake, which produced relatively weak

ground motion shaking but generating tsunami, is indispensable. Otherwise, they may perform falseresponse and causes high fatalities.

Table 1 Part of Timeline: July 17, 2006 Java, Indonesia Earthquake and TsunamiCompiled by IOC ITIC (Local time set was added by the author)

No. UTC Local Elapsed

Time Action

1. 08:19 15:19 0:00 Earthquake occurs (USGS and Harvard CMT: 9.28S, 107.38E, 34 km, Mw7.7)

2. 08: 21 15: 21 0:02 BMG calls start to be received

3. 08: 24 15: 24 0:05 BMG SMS alertreporting automatic solution using 8 stations, ML6.8

4. 08: 25 15: 25 0:06 BMG Mb5.5 => large difference in M implies non-typical earthquake.

PTWC Seismic Alarmtriggers alerting PTWC duty staff.

5. 08: 26 15: 26 0:07 BMG press inquiry on phone and issued to media - caution for tsunami.

JMA Operations Trigger for Distant Earthquake.

6. 08: 27 15: 27 0:08

BMG unsuccessful to contact local government official in the coastal area by telephone dueto unavailability of communication contact points at the said areas. SMS message sent tolist of about 400 available addresses, though list did not contain many Java coastaladdresses

7. 08: 29 15: 29 0:10 NEIC Short Period Alarm

8. 08: 31 15: 31 0:12

PTWC Observatory Message with preliminary epicenter (9.3S, 107.3E), ma nitude Mw

7.3) and P-wave arrival times disseminated to other observatories (e.g., JMA, WC/ATWC)9. 08:32 15:32 0:13 JMA receives PTWC Observatory Message

10. 08: 33 15: 33 0:14 WC/ATWC calls to PTWC (determines that WC/ATWC does not need to issue a bulletin

since the earthquake is not in the Pacific Ocean)

11. 08: 36 15: 36 0:17

PTWC Bulletin #1- Indian Ocean Local Tsunami Watch Message disseminated via GTS,email, fax, putting Indonesia and Australia in a Watch, M 7.2; roviding estimated tsunamiarrival times for tsunami forecast points at Christmas Island, Australia (0836), Cilacap,Indonesia (0900)

NEIC initial automatic solution, Mwp 7.2

12. 08:38 15:38 0:19 JMA receives PTWC Bulletin #1

13. 08:39 15:39 0:20 PTWC confirms with Emergency Management Australia by Telephone

14. 08: 40 15: 40 0:21 Tsunami arrival, Pangandaran, ..

MENTAWAI TSUNAMI 2010 AND DISASTER PREPAREDNESS FOR SMALL ISLANDS

Mentawai tsunami 2010 was generated by a tectonic earthquake (Mw=7.8) occurred on 25 October

2010 at 21:42 local time seaward of the Mentawai Islands, off-shore of Sumatra. Tsunami run-up of 3to 9 m struck along southwestern coasts of the Pagai Islands and took 530 lives. Figure 10 shows

location map of Mentawai Islands and the epicenter of the 2010 tsunamigenic earthquake.Tsunami Mentawai on October 25, 2010 gaves another prove of the urgency of an effective

telecommunication and transportation system during disaster, especially when dealing with remote

islands like Mentawai. Unavailability of this system was considered as one of the root of the lateemergency response in this disaster. The importance of integrated operation and maintenance of

tsunami early warning system was also learnt from this disaster event.

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Table 3 Initial response timeline to the Mentawai tsunami

LOCAL

TIME

10/25 10/26 10 /27

21:42

21:4721:48

21:49

22:01

22:23

22:25

22:3422:43

23:20

23:42

00:20

03:10

04:30

08:00 20:00 morning

TIME

ELAPSED

5'

6'

7'

19'

41'

43'

52'

1hr

01'

1hr

38'

2hr

00'

2hr

38'

5hr

28'

6hr

48'

10hr 18' 22hr 34hr

NEIC-EQrecord

ed

PTWC-EQmess

age

PTWC-tsunami

watch

JMA-tsunamiw

atch

BMKG-Enggano

;0.2

7m

BMKG-Padang;0.3m

JMA-Padang;0

.3m

PTWC-tsunami

watch

cancelled

JMAPadang,e

tc.;

0.2m

0.4m

oJakartaMentawaiIslands

Malaysia

Q Epicenter

(USGS, 2010)

INDIAN

OCEAN

SiberutIsland

ipora

Island

agai Selatan

Island

oPadang

Fig.10 Map of the earthquake epicenter location

agai Utara

Island

30 km

No feedback

confirmation from

Mentawai;

telecomunication

system failed

Provincial Gov. got the disaster

report by a courier come from

Mentawai by motorboat:

Emergency response STARTED

National coordination

meeting for emergency

Emergency response by

using six helicopters

bad weatherhampered the

emergency response; several

dispatchedemergency ships

were retur ned backto Padang

12 hrs

BMKG: sunami Warning!!

- sent to media & local gov,

including Mentawai

BMKG: arning CANCELLED!!

- no destructive tsunami

Actual initial

tsunami arrived

in 5-10 minutes;

1 to 9m tsunami

depth

BMKG Simulation:Tsunami will attackPagai Selatan at21:49:52

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Initial response timeline to Mentawai tsunami

In reference to the International Tsunami Alert Service Timeline released by UNESCO/IOC (2010),

Mentawai earthquake and tsunami timeline by BMKG Indonesia (2010) and compiled internet onlinenews, an initial response timeline to the Mentawai tsunami is summarized in Table 3.

Table 3 informs several facts related to the response situation at the initial state of Mentawai

tsunami as follows:1. Based on numerical simulation result, the Meteorological, Climatological and Geophysical Agency

of Indonesia (BMKG) concluded that tsunami was generated and will attack Pagai Selatan Island atabout 21:49:52. Accordingly, BMKG released tsunami warning 5 minutes after the earthquake

through electronic media as well as direct message to the local governments including Mentawai.

This warning was cancelled 47 minutes later since no feedback confirmation from the Mentawailocal government about the actual field situation and tide-gage measurement network informed

small tsunami amplitude (0.2 0.4m).

It was known later that the telecommunication system failed to work since the electricity down dueto the lack of fuel to feed the electric generator in the central telecomunication station. In fact,

Mentawai Islands were regularly lack of fuel supply to support the daily activities.

2. The first courier from Mentawai Island arrived at Padang City in the next morning af ter 6 hourstough motorboat journey under the bad sea climate and weather to report about the disaster

situation.

3. Immediately after receiving the actual disaster information, emergency responses were started bythe Provincial Government of West Sumatera. However, severely bad sea climate and weather

hampered the emergency response; several dispatched emergency ships were returned back to

Padang;4. A national level emergency coordination meeting was held in the evening of the same day to get

decission on the mobilization of helicopters for supporting the emergency measures, but the actual

actions were started only on the next day morning.

Risk Knowledge, Local Awareness and Fatalities Reduction

A field observation and questionaire survey were carried out in Mentawai Islands after the tsunami of

October 25th, 2010. Field observation was done to investigate if land use management interventionregarding tsunami mitigation has been implemented, whereas questionaire survey was directed to

collect information related to the evacuation processes, by using key questions such as background

situation of evacuation decission, knowledge on tsunami, tsunami inundation depth at the initialdecission of evacuation, ect. Survey locations include Surat Aban, Tapak, and Malakopa Villages in

Pagai Selatan District, and Sabeugungung, Montei Teikaku, Montei Baru-baru, and Betumonga in

Pagai Utara District.Among the interesting result from the questionaire survey is that 40% of respondent have known

about tsunami and its characteristics before the latest event, whereas 32% have never known before

and 23% have heard about but not really understand. Regarding the timing of evacuation decission,

about 49% respondent did just after sensed the earthquake, 20% did after heard the shouting forevacuation, 15% after seeing that other people runaway, and each are 5% after observing the sea water

rise or recede respectively.

CONCLUSIONS

Tsunami intensity has a potential to be used as hazard identification based on which disastermitigation activities can be determined easier.

In the near future, while continuing the development of the whole tsunami disaster mitigation

system, the public education on the accurate knowledge of tsunami danger and various precursorsmust be intensively and extensively carried out, by which individual awareness as well as community

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preparedness can be sustainably developed in the whole tsunami prone area to minimize the impact oftsunami disaster.

REFERENCES

Edward Bryant, Tsunami the Underrated Hazard, 2nd Edition, 2008, Springer, pp.132-133

Mori, J., Mooney, W. D., Afnimar, Kurniawan, S., Anaya, A.I., Widiyantoro, S. (2007). The 17 July2006 Tsunami Earthquake in West Java, Indonesia.Seismological Research Letters, Vol. 78, No. 2,201-207.

Muhari, A., Diposaptono, S., Imamura, F. (2007). Toward an Integrated Tsunami Disaster Mitigation:Lessons Learned from Previous Tsunami Events in Indonesia.Journal of Natural Disaster Science,Vol. 29, No. 1, 13-19.

Lay, T., C. J. Ammon, H. Kanamori, Y. Yamazaki, K. F. Cheung, and A. R. Hutko (2011), The 25

October 2010 Mentawai tsunami earthquake (M w 7.8) and the tsunami hazard presented by

shallow megathrust ruptures, Geophys. Res. Lett., 38, L06302, doi:10.1029/2010GL046552

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